This invention relates to the field of transportation of goods, and more particularly to "tie-downs", or means for securing loads to the flatbeds of vehicles particularly such vehicles which do not have end bulkheads or other laterally extending restraining members against which the loads can be secured. The customary procedure involves passing chains, cables, ropes, steel bands, or other flexible equivalents, hereinafter referred to generally as "lashings", over the tops of the load elements and securing them to eyes, rings, clevises, or stake pockets with which the sides of the cars are equipped.
Little difficulty is encountered in restraining loads against vertical or transverse movement, but preventing longitudinal shift of loads is not easy, particularly for railroad vehicles where longitudinal impacts due to switching and transportation are numerous and severe. Provision of bulkheads at the ends of such cars offers a partial solution, and temporary cross members have also been proposed. The tremendous forces required to arrest the movement of a load of many tons, once it has begun to shift, make these expedients less than wholly satisfactory.
One factor that demands consideration in this connection is that many loads tend to compact or settle during transportation, so that an initially tight securing arrangement or "tie-down" gradually loosens. Recognition of this factor has led to the provision of resilient tie-down accessories through which the lashing materials can be passed at one or both sides of the car. If the lashing is secured under sufficient tension to strain the resilient accessory adequately, a considerable amount of load compaction can occur without undue loosening of the tie-down arrangement.
An increasingly popular lashing is steel strapping or banding. This material is available in widths between half an inch and three inches, the gauge of the metal naturally varying with its width. Banding is convenient to use, in appropriate sizes, and efficient instruments have been developed for securing it around a load under considerable tension. U.S. Pat. No. 3,678,866 to O'Leary et al. shows how banding can be used both to form material to be shipped into bundles for efficient handling, and to secure the bundles on the bed of a flat car. The tie-downs disclosed in that patent comprise steel bands passing at both sides of the car around the pins of clevises connected by spring assemblies and chains to the side sills. When the bands are tensioned to three thousand pounds, for example, an apparently very secure loading system results.
Experience has shown, however, that there is an undesireably high incidence of failures in tie-downs of this sort. The failures are observed to occur by tearing of the band material where is passes around the clevis pins.